Chapter 2. Immunodeficiencies
The pediatrician should be aware that there are a number of rare disorders that may present with an eczematous eruption similar to atopic dermatitis.

Primary immunodeficiencies, such as severe combined immunodeficiency (SCID) can present with erythroderma (diffuse redness usually associated with scaling). These infants, as opposed to otherwise healthy atopic dermatitis infants, will usually have other signs of systemic illness such as failure to thrive, chronic diarrhea and/or recurrent infections.

Wiskott-Aldrich syndrome is an X-linked disorder that may result in an extremely pruritic, diffuse eczematous dermatitis. The rash of Wiskott-Aldrich may be more hemorrhagic in appearance than atopic dermatitis, with petechiae and sanguinous crusts predominating, likely due to the platelet abnormalities associated with the disorder.

The hyperimmunoglobulin E (IgE) syndrome is an immunodeficiency syndrome that may present with an eczematous dermatitis. In the hyper-IgE syndrome, the rash resembles atopic dermatitis but inflammatory facial papules may be the predominant morphology, helping to distinguish the two disorders. Skeletal and dental anomalies are also seen and patients often have repeated fractures and retained primary teeth. Very high levels of serum IgE (>2000 mg/dl) are seen with this disorder, although patients with severe atopic dermatitis may have equally high levels.